Remove support for a default identity (or alias) path

[str4d]

Instead of configuring defaults, users should specify identity files directly.

[codecov]

Codecov Report

Merging #152 (3bacabc) into master (52e5377) will increase coverage by 0.11%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #152      +/-   ##
==========================================
+ Coverage   39.42%   39.53%   +0.11%     
==========================================
  Files          25       25              
  Lines        2042     2036       -6     
==========================================
  Hits          805      805              
+ Misses       1237     1231       -6     

Impacted Files	Coverage Δ
age/src/cli_common.rs	0.00% <ø> (ø)
rage/src/bin/rage-mount/main.rs	0.00% <0.00%> (ø)
rage/src/bin/rage/error.rs	0.00% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 52e5377...3bacabc. Read the comment docs.